1. Field of the Invention
This invention pertains to bore hole drilling apparatus and more specifically to that part of such apparatus known in the industry as a roller-reamer.
2. Description of the Prior Art
Roller-reamers have been employed in earth boring operations for the petroleum industry to provide two main functions. Depending upon the particular structure, these functions may be provided in a combination tool or the functions can be provided separately.
The first function that is provided by a roller-reamer is to cut formations to enlarge the hole to the desirable size, which may be the original size of the bit in the case where the bit wears to be under-gauged. However, even for new bits, roller-reamers are employed to cut formations because the bit does not always drill a true bore hole and because of slight lateral shifting which is inherent in the drilling operation, which shifting leaves ledges and other distortions.
The second function of a roller-reamer is to keep the drill stem in the center of the hole at the specific position of placement of the roller-reamer. In providing such a function, a reamer is often referred to as a "stabilizer". Maintaining the drill stem centered has many beneficial effects, its primary one being minimizing unintentional hole-angle directional drilling.
Generally speaking, a roller-reamer will always include the following parts: (1) Threaded connections at each end of the body for connection into the drill string at either end of the reamer. (2) Rollers and shafts (sometimes referred to as "cutters and pins") with axial and radial bearings. It should be noted that virtually all reamers have shafts extending through the rollers with the radial bearings being located between the two. In some instances, a trunnion design with a shaft integral with the roller and extending on each end of the roller is provided. In such case, the shafts rotate with the roller in sockets. (3) Fluid circulation passage through a hole in the center of the body.
Popular hole sizes for well bores range from 5" to 26" in diameter. Size of circulation passage through the center of the body of the reamer typically range from 11/2" to 31/4" in diameter. The body size on the necks beyond the area where the rollers are mounted typically range from 41/8" to 11" in diameter. This latter size will normally be the same size as the drill collar. Body links normally range from 4' to 8'.
Most roller-reamers have three rollers equally spaced in a single transverse section. Such roller-reamers are referred to as "3-point reamers". When two sets of three rollers spaced apart longitudinally are used, the roller-reamer is called a "6-point reamer". However, large diameter roller-reamers may have more than three rollers in one transverse section.
For purposes of discussion herein, a "roller-reamer unit" will refer to a single shaft, roller and related parts and "roller-reamer" will refer to the entire assembly of three or more roller-reamer units.
Bearing surfaces are normally case hardened, usually by the process of carborizing, quenching in oil from austinite at about 1500.degree. F. When the roller or cutter is to be used for difficult reaming operations, the outer surface or cutting structure will have pressed fitted therein sintered tungsten carbide compacts for the cutting structure. However, when the roller is to be used mostly as a stabilizer, and only light reaming operations are to be encountered the outer surface may only be carborized and hardfaced with tungsten carbide particles.
In all events, most of the roller-reamer component parts are designed and manufactured to be replaceable so that as wear occurs, the worn parts are discarded and new parts are installed on the tool. It is desirable that the construction be such that the most expensive parts do not have to be replaced any more often than necessary. Also, it is desirable that the construction be such so as to minimize excessive wear from occurring in the first place under the environmental conditions of use. It should be remembered that a roller-reamer is subjected to extremely abusive conditions during its use by the very nature of such use. For example, this abuse results from twisting of the drill string and resistance thereto, longitudinal surges in handling the drill string and from the pressures of the formation and the fluids introduced for drilling purposes, from the variations in the lithological conditions encountered while drilling and in handling of the string for maintenance, repairs and non-drilling operations (e.g., removal for logging purposes, fishing purposes and the like).
It has been known that a condition imposed on the drill string known as "fretting" is one of the worse conditions that causes wear of the roller-reamer parts. Fretting is the small vibration act that constantly occurs in operation because of the many conditions imposed on the drill string during drilling. Fretting occurs in an up and down, back and forth motion and in a rotational motion all at once. To ensure minimum wear between adjoining parts, it is desirable to fixedly secure together as many parts as possible and to minimize the number of parts that have to move with respect to each other in the first place. In so doing, the places where fretting has an opportunity to occur is kept to a minimum. But, for places where it is not possible to fix one part to another, then it is desirable to have a bearing surface between such parts. Since some parts of a roller-reamer are rotational with respect to one another by their very nature, such parts cannot be fixed to each other. Other parts cannot be rigidly joined because they have to accept impacts beyond the flexure capability of the metal alone. Absence of such capability would cause premature damaging fatigue and fracture. Yet other parts cannot be permanently fixed or joined or eliminated in a simplified structure because they have to be non-destructively removable to facilitate replacement of worn parts.
It cannot be over-emphasized that roller-reamer assemblies are notoriously short-lived because of the extremely hard wear to which they are subjected, which wear is exerted on the assembly in all possible conceivable patterns and directions. As is explained hereinafter the embodiments of the present invention reduce the number of component parts compared with the prior art while maintaining tight fitting of those parts that do not have to have relative movement, providing bearing surfaces for those that do. In addition, by making some parts reversible, the effective life of many that do wear out is extended greatly. Furthermore, the embodiments presented herein also do not subject parts, other than the roller part itself, to gauge wear. That is, all other components are well within the outer limits of the outside diameter of the roller.
Perhaps the largest contribution of the present invention, therefore, is the virtual elimination of two types of wear occurring in prior art structures. Wear occurs during use in such structures (1) at the outside of the roller, (2) at the inside surface of the roller, (3) at the outside periphery of the shaft underneath the roller, (4) at the outside surface of the shaft inside the blocks, and (5) at the inside surface of the blocks. The latter two wear conditions are a result of fretting under dynamic loads. Fretting is almost totally eliminated in the embodiments of the present invention described hereinafter, and, hence, so are the types of wear that would normally accompany fretting.
The most relevant designs known prior to the present invention are shown and described in U.S. Pat. No. 4,182,425. These designs include a roller-reamer unit having a replaceable block structure for holding the shaft around which the cylindrical roller rotates (FIG. 1); a similar structure having a thrust bearing between the roller and the block (FIG. 1A); a similar structure wherein the shaft is welded to the block, the shaft also being flanged for accepting an axial thrust impact (FIG. 1B); and a similar structure wherein the upper block is welded to the shaft, there being a thrust flange or bearing and there being reservoirs for lubricating between sealed, relatively rotational components of the structure (FIGS. 9, 9A, 9B, 9C and 9X). The other structures of '425 related to roller-reamers having air bearings and are not relevant to the present invention.
The blocks used in the embodiments disclosed in '425 are expendable components which wear with use because of fretting and otherwise. Although such blocks facilitate replacement, having to throw away previously used blocks contributes substantially to the cost of using a roller-reamer. In the roller-reamers employing a sealed bearing construction, the top block is expended each time a roller and shaft is worn out because the block is welded to the shaft.
Also, in the sealed bearing roller-to-shaft construction of the '425 patent, the lower block must protrude beyond the body diameter in order to protect the lower seal between the roller and shaft in a heavy reaming operation. Especially in such an embodiment but in the case of all of the lower blocks employed in the embodiments shown in the '425 patent, the outer surface of such blocks are subjected to wear during the reaming operation. Such wear is a result of fretting at the shaft contact and at the points of wear engagement of the outer surface with the borehole.
Experience has shown that with all of the non-sealed constructions of patent '425, both top and bottom blocks must be replaced by the time two or three sets of rollers and their shafts are worn out as a result of the types of wear mentioned above and because of wear resulting from the thrust of the reamer in action.
The prior art also reveals a system for tightening the shaft of a roller-reamer unit into the body in such a manner to presumably tightly hold it, but this technique critically fails to cause uniform securing and therefore invites non-uniform wear and fretting after short periods of use. In this system, the end of the shaft is split. A block having a transverse tapered pin is forced over the shaft end, the pin acting within the slot to force the end of the shaft apart against the inside surface of the block. The block is then welded in place. The tapered pin successfully tightens the end of the shaft against the block at the two points normal to the axis of the pin. But, the pin does not successfully tighten the shaft end at locations remote from these two points, thereby inviting wobble and uneven wear. Further, welding the block means it must be destroyed each time the shaft is replaced.
Therefore, it is a feature of the present invention to provide an improved roller-reamer apparatus wherein each replaceable roller-reamer unit employs either no blocks or few block parts, and wherein the unit is otherwise completely tightly fitted within the body of the roller-reamer and the moving parts are protected with radial and thrust bearings.
It is another feature of the present invention to provide an improved roller-reamer unit wherein the shaft is replaceable but tightly fitting with the body, thereby eliminating wear attendant to fretting.
It is still another feature of the present invention to provide an improved roller-reamer unit having releasable shaft blocks, the shaft tightly fitting with the blocks and the blocks within the body, thereby achieving wear-elimination of the blocks because of fretting.
It is yet another feature of the present invention to provide an improved roller-reamer unit having a block that does not radially protrude beyond the limits of the roller portion.
It is still another feature of the present invention to provide an improved roller-reamer unit with an internal lubrication reservoir, the lubrication being provided between the shaft and the reamer, the lubricated portion being sealed substantially at both the upper and lower ends of the roller.
It is yet another feature of the present invention to provide an improved roller-reamer unit having roller bore hole contacts below the lower lubricating seal to provide protection therefor.
It is still another feature of the present invention to provide an improved roller-reamer unit shaft that is 180 radial degrees reversible for extending the effective useful life of such shaft.